SOI device with contact trenches formed during epitaxial growing

ABSTRACT

A method for manufacturing an integrated electronic device. The method includes providing an SOI substrate having a semiconductor substrate, an insulating layer on the semiconductor substrate, and a semiconductor starting layer on the insulating layer; epitaxially growing the starting layer to obtain a semiconductor active layer on the insulating layer for integrating components of the device, and forming at least one contact trench extending from an exposed surface of the starting layer to the semiconductor substrate before the step of epitaxially growing the starting layer, wherein each contact trench clears a corresponding portion of the starting layer, of the insulating layer and of the semiconductor substrate, the epitaxial growing being further applied to the cleared portions thereby at least partially filling the at least one contact trench with semiconductor material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the electronics field. Morespecifically, the present invention relates to integrated electronicdevices of the Silicon On Insulator (SOI) type.

2. Discussion of the Related Art

Electronic devices of the SOI type are integrated in a composite wafer,in which a buried insulating layer (such as of silicon oxide) separatestwo semiconductor layers (such as of mono-crystalline silicon).Particularly, the lower (thicker) silicon layer defines a commonsubstrate; the upper (thinner) silicon layer acts as a starting layer,which is grown epitaxially to obtain an active layer housing thedifferent electronic components (such as, MOSFET transistors) of the SOIdevice.

The oxide layer provides a robust voltage insulation of the componentsin the active layer from the substrate. Moreover, DTI (Deep TrenchIsolation) processes may be efficiently employed to provide lateralinsulation from adjacent components that are integrated in the same SOIdevice within different insulated regions of the active layer. Inparticular, such regions are fully insulated by means of the (buried)insulating layer and the DTI trenches. In addition, standard LOCOS(Local Oxidation of Silicon) or STI (Shallow Trench Isolation) processesmay be used to provide a further lateral insulation of the componentsthat are integrated in the same insulated region. Moreover, the SOIdevices have other important advantages. For example, they do not sufferleakage effects between adjacent components. Moreover, the parasiticcapacitances of the components integrated in the SOI device aresignificantly reduced.

Usually it is desired to maintain the substrate at a predeterminedvoltage (for example, to avoid undesired capacitive coupling effects).Particularly, when the substrate is not directly accessible from thebackside of the SOI device it needs to be biased to the desired voltagethrough a corresponding contact formed on a front (upper) surfacedefined by the active layer. A typical example is an SOI device that ismounted on a chip carrier with a flip-chip technique, wherein the frontsurface of the SOI device faces the chip carrier (with its contacts thatare directly connected to corresponding bumps of the chip carrier).

For this purpose, a via hole (or simply via) crossing the insulatinglayer of the SOI wafer is provided so as to connect the two siliconlayers (i.e., the active layer and the substrate). Typically, the via isformed in a dedicated insulated region of the active layer and isconnected to a corresponding contact arranged on the front surface.

In the state of the art such via is obtained by selectively etching theactive layer so forming a trench extending from the front surface downto the substrate. The walls of the trench are then covered by aconformal conductive layer (i.e., such as to substantially follow theprofile of the underlying structure), which conductive layer furtherextends on the front surface so as to define the desired contact.

A drawback of the solution described above is that each trench consumesa significant area of the SOI device. In fact, the trench must be wideenough to ensure that the conductive layer uniformly covers all itswalls so resulting conformal (i.e., the trench has a significantso-called “step coverage”). This significantly increases the size of thewhole SOI device.

A further problem of the SOI wafer is that the active layer can beaffected by impurities, which impair the performance of the electroniccomponents that are housed therein (and then of the whole SOI device).

In addition, the SOI wafer is typically used to integrate high-voltageelectronic components (e.g., able to sustain voltages ranging from 50Vto 250V); however, the same structure is not well suited to houselow-voltage electronic components (e.g., able to sustain voltagesranging from 1.8V to 3.3V), for which a standard wafer with PN-junctioninsulation would be preferred. This problem is particularly acute fordevices requiring both low-voltage and high-voltage electroniccomponents.

SUMMARY OF THE INVENTION

In principle, the present invention is based on idea of providing one ormore contact trenches across the insulating layer.

One embodiment of the present invention proposes a method formanufacturing an integrated electronic device. The method starts withthe step of providing an SOI substrate; the SOI substrate comprises asemiconductor substrate, an insulating layer on the semiconductorsubstrate, and a semiconductor starting layer on the insulating layer.The starting layer is then epitaxially grown to obtain a semiconductoractive layer on the insulating layer (for integrating components of thedevice). The method further comprises forming one or more contacttrenches extending from an exposed surface of the starting layer to thesemiconductor substrate before epitaxially growing the starting layer;each contact trench clears a corresponding portion of the startinglayer, of the insulating layer and of the semiconductor substrate. Theepitaxial growing is then further applied to the cleared portions,thereby at least partially filling the contact trenches withsemiconductor material.

According to one embodiment of the invention, an implantation process isused to form an interface region enclosing the contact trenches.

Advantageously, this result is achieved by means of one or more beams ofimpurities, which are tilted with respect to an axis of each contacttrench.

In one embodiment of the invention, the proposed solution is used toform a front-rear contact across the insulating layer. In this case, theinterface region is a contact region (of the same type of conductivityas the semiconductor substrate and the active layer, but with a higherconcentration of impurities); a further contact region extends from afront surface of the device (wherein a corresponding electrical contactis formed) to a (buried) contact region.

As a further enhancement, a contact window on the front surface (for theelectrical contact) is spaced apart from an axis of each contact trench.

A preferred quantitative definition of this displacement is alsoproposed.

In another embodiment of the invention, the interface region gettersimpurities of the active layer (which impurities are then segregated byinsulating a gettering region including it).

Advantageously, in both cases multiple contact trenches are formed.

A preferred layout of those contact trenches is also proposed.

In another embodiment of the invention, the devised solution is used tocreate a selective SOI device. In this case, the interface region is aninsulating region (of the opposite type of conductivity with respect tothe active layer); an insulating trench enclosing it defines an activeregion based on PN-injunction insulation (such as for integratinglow-voltage components or components that have to dissipate heat throughthe semiconductor substrate), whereas the remaining portion of theactive layer maintains the SOI structure (such as for integratinghigh-voltage components or components that need fast access time, lowleakage and low parasitic capacitance).

Another aspect of the present invention provides a correspondingelectronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, as well as further features and the advantagesthereof, will be best understood by reference to the following detaileddescription, given purely by way of a non-restrictive indication, to beread in conjunction with the accompanying drawings. In this respect, itis expressly intended that the figures are not necessary drawn to scaleand that, unless otherwise indicated, they are merely intended toconceptually illustrate the structures and procedures described herein.Particularly:

FIGS. 1A through 1I are cross-section views illustrating the main phasesof the manufacturing process of an electronic device, according to afirst embodiment of the present invention;

FIG. 2 shows a partially cut-away elevation view of this electronicdevice;

FIG. 3 shows an exemplificative diagram relating to electrical operativeparameters of the same electronic device;

FIGS. 4A through 4B are cross-section views illustrating the main phasesof the manufacturing process of an electronic device, according to asecond embodiment of the present invention; and

FIGS. 5A through 5F are cross-section views illustrating the main phasesof the manufacturing process of an electronic device, according to athird embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1A through 1I, a process is described formanufacturing an electronic device 100 (see FIG. 1I) with a front-rearcontact according to a first embodiment of the present invention.

Considering in particular FIG. 1A, the starting material is an SOIsubstrate 105. The SOI substrate includes a semiconductor substrate 110(for example, of the N-type of conductivity with a resistivity rangingfrom 1 cm to 500 cm, such as 400 cm). Moreover, the SOI substrate 105includes a semiconductor starting layer 112 of the N-type, which isseparated from the (semiconductor) substrate 110 by an insulating layer115. For example, the insulating layer 115 has a thickness ranging from0.1 μm to 2 μm, and preferably from 0.5 μm to 1.5 μm (such as, 1 μm),whereas the starting layer 112 has a thickness ranging from 50 nm to1.500 nm.

Moving now to FIG. 1B, one or more contact trenches 120 (such as amatrix of 9 contact trenches 120, three of which shown in the figure)are formed by selectively etching the layers 112 and 115. For thispurpose, a photoresist mask 122 is provided on top of the starting layer112, so as to leave exposed areas thereof where the contact trenches 120are desired. Using suitable etching techniques, the layers 112, 115 areselectively removed, down to the substrate 110.

The etching of the layers 112, 115 is performed by two processes, whichare substantially anisotropic along a vertical direction Y—perpendicularto the layers 112, 115 (meaning that the layers 112, 115 are etched onlyvertically). The first etching process selectively removes the areas ofthe starting layer 112 which are left exposed by the photoresist mask122. Then, the second etching process selectively removes the insulatinglayer 115 in the same areas down to the substrate 110.

In such a way, each contact trench 120 clears a corresponding upperportion of the substrate 110 (defining a bottom wall 130 b) andcorresponding internal portions of the starting layer 112 and of theinsulating layer 115 (defining side walls 130 s).

As shown in FIG. 1C, a dopant implantation is performed in order to formheavily doped internal regions 140 within the substrate 110 and thestarting layer 112 (only shown for the substrate 110 in the figure). Forexample, in order to form N+ internal regions 140, Arsenic (As),Antimony (Sb) or Phosphorus (P) dopant ions are used; preferably, thedopant dose ranges from 10¹² ions/cm² to 10¹⁶ ions/cm². Suchimplantation is performed with the photoresist mask 122 still in place,so as to have the internal regions 140 in zones corresponding to thecontact trenches 120.

For this purpose, two (or more) dopant implantation processes areperformed along different directions, in order to cause desired dopantions to penetrate the sidewalls 130 s of the starting layer 112 and thebottom walls 130 b of the substrate 110. Particularly, each implantationprocess involves the use of a beam of dopant ions propagating along adirection I having a corresponding tilt α with respect to the verticaldirection Y. Preferably, the tilt a ranges from 2° to 45°, and morepreferably from 5° to 20° (such as α=7°). Preferably, two implantationprocesses are performed along directions that are symmetric with respectto the vertical direction Y (so as to reach opposed regions). Forexample, during a first implantation process the wafer is inclined withrespect to the direction of the dopant ions beam at an angle α=7°,whereas during a second implantation process the wafer is inclined atthe opposite angle α=−7°.

The photoresist mask 122 is stripped at the end of the implantationprocesses. Referring now to FIG. 1D, an epitaxial growing process isthen carried out (for example, by means of Vapor-Phase Epitaxy). Theepitaxial growing process is performed in a room comprising a siliconcompound (for example, silicon tetrachloride SiCl₄ or trichlorosilaneSiHCl₃) at high temperature (for example, ranging from 1000° C. to 1200°C.). The epitaxial growing process applied to the starting layer 112(shown in FIG. 1C) results in the generation of an active layer 142 ofthe N-type (for example, with a thickness of about 1 μm-10 μm).

Concurrently, the same epitaxial growing process applied to the walls130 b and 130 s (again shown in FIG. 1C) at least partially fills thecontact trenches 120, possibly leaving vacant regions 143 therein. Thiseffect is due both to the geometry of the contact trenches 120 and tothe different growing rates of the epitaxial growing process over thecleared portions of the substrate 110, of the insulating layer 115 andof the starting layer 112 (shown in FIG. 1C). As a result, the obtainedstructure may be not planar, with recesses corresponding to the contacttrenches 120 on its front (upper) surface 150. In order to reduce thisnon-planarity (which may lead to an electrical discontinuity of thefinal structure), the layout of the contact trenches 120 is finely tunedtaking into account the epitaxial growing process parameters (asdescribed in detail in the following).

During the epitaxial growing process, the dopant ions of the internalregions 140 (shown in FIG. 1C) diffuse thereby forming a contact region145 of the N+ type. As can be noted, the contact region 145 encloses allthe contact trenches 120 (across the insulating layer 115) so as toelectrically couple the substrate 110 with the active layer 142. Thecontact region 145 is more conductive than the semiconductor materialsurrounding it, due to the high dopant concentration created by theabove-mentioned diffusion.

Moving to FIG. 1E, a field oxide layer 155 is formed (for example, bymeans of a selective or LOCOS thermal growth) in order to cover thefront surface 150 of the active layer 142—except for a portion thereofwhere active areas 157 of the desired front-rear contact will bedefined. For this purpose, a silicon nitride (such as Si₃N₄) mask—notshown in the figure—is provided on top of the active layer 142, so as toleave exposed areas thereof where the field oxide layer 155 is to begrown.

Continuing to FIG. 1F, one or more insulating trenches 158—for example,of the DTI type—are then formed. For this purpose, another photoresistmask 159 is provided on top of the field oxide layer 155 and of theactive layer 142, so as to leave exposed areas thereof where theinsulating trenches 158 are desired. Using suitable etching techniques,the active layer 142 and the field oxide layer 155 are selectivelyremoved, down to the insulating layer 115. As a result, the insulatingtrenches 158 partition the active layer 142 into insulated regions 160,which will be used to integrate the desired electronic components.Moreover, the insulating trench 158 around the contact trenches 120defines an (insulated) active region 161, which is used to contact thesubstrate 110 from the front surface 150 so as to provide the desiredfront-rear contact through the insulating layer 115.

For this purpose, the mask 159 is stripped away. Continuing to FIG. 1G,the insulating trench 158 is filled with dielectric material, such assilicon-dioxide (for example, by means of CVD oxide deposition).Thereafter, an implantation process is performed (through the activeareas 157) in order to obtain a heavily doped region within the activeregion 161; in the example at issue, As or P dopant ions are used. Then,the dopant ions diffuse so forming an N+ contact region 170, whichextends from the front surface 150 to the (buried) contact region 145.

Moving to FIG. 1H, a dielectric layer 175 (for example, doped siliconoxide) is deposited on top of the field oxide layer 155 and on theactive areas 157, for example, by means of a CVD process. Then, thedielectric layer 175 is planarized, typically using the CMP (ChemicalMechanical Polishing) technique, so as to flush the recessescorresponding to the contact trenches 120 formed beforehand.

As shown in FIG. 1I, a plurality of contact windows 185 are etched inthe dielectric layer 175 in correspondence of the active areas 157 (soas to reach the contact region 170). Preferably, each contact window 185surrounds the contact region 145 in plant view. Particularly, each pointof the contact window 185 is spaced apart from an axis A of each contacttrench 120 (parallel to the vertical direction) in order to prevent anydisturbances due to the corresponding recesses on the front surface 150.Preferably, a line B connecting each point of the contact window 185 (atthe corresponding active area 157 on the front surface 150) with theedge of the contact trench 120 closest to the contact window 185 (on itsbottom wall at an upper surface of the substrate 110) forms an angle β,which is higher than 60°, preferably at least equal to 61°-85°, and morepreferably at least equal to 64°-82° (such as at least equal to 65°). Inother words, this condition needs to be satisfied by the internal edgeof the contact window 185, with respect to the contact trench 120 thatis closest to the contact window 185 (being the same angle higherotherwise).

Afterwards, a metallization layer 190 (for example, Al or Ti/TiN plus aW-plug and an Al layer) is deposited on top of the wafer, therebyfilling the contact windows 185 and covering the exposed surface of thedielectric layer 175. The metallization layer 190 is then shaped todefine a pad. In such a way, the desired electronic device 100 isobtained; the electronic device 100 includes the required front-rearcontact, which allows contacting the substrate 110 from the frontsurface 150 (for example, to bias the substrate 110 at a predeterminedvoltage in flip-chip applications). More specifically, this front-rearcontact is obtained through the pad 190, the contact windows 185 (thehigher the number of contact windows 185, the higher the conductivitythereof, the contact region 170, and the contact region 145.

The front-rear contact described-above has a small size (compared to thesolutions known in the art); this has a beneficial effect on the amountof area taken up by the whole electronic device 100. Moreover, thisresult is achieved without adversely affecting the electrical propertiesof the front-rear contact, especially its resistance.

Particularly, several factors contribute to the desired characteristicsof the front-rear contact. For example, a contribution is given by thecontact region 145; particularly, its beneficial effect is emphasized bythe fact that the contact region 145 surrounds the contact trenches 120.This is achieved thanks to the corresponding implantation processes thatare tilted as indicated above (with the best result provided by theproposed angles).

In addition, the choice of displacing the contact windows 185 withrespect to the axis of the contact trenches 120 creates a preferentialpath for the electrical charge along which the resistance of thesemiconductor material is further reduced (with the best results thatare provided by the proposed angles).

Moving to FIG. 2, a partially cut-away elevation view of theabove-described electronic device 100 is shown. As can be noted, theinsulating trench 158 defines the active region 161 for the front-rearcontact. The active area 157 for the contact windows within the activeregion 161 surrounds the contact region 145 around the contact trenches120.

Preferably, each contact trench 120 has a square transversal sectionwith each side (denoted with 1) ranging from 1.5 μm to 5 μm, and morepreferably from 2 μm to 4 μm (such as 3 μm). The contact trenches 120are arranged in a matrix (with three rows and three columns in theexample at issue). Particularly, each contact trench 120 is spaced apartfrom any adjacent contact trench 120 by a distance (denoted with s),which preferably ranges from 1 μm to 3 μm, and more preferably from 1.2μm to 2.5 μm (such as 1.5 μm).

The proposed layout of the contact trenches 120 allows reducing theabove-mentioned electrical discontinuities of the electronic device 100(due to the non-planarity caused by the contact trenches 120). Moreover,this arrangement of the contact trenches 120 has been found to provideoptimum results (in terms of the lowering of the front-rear contactresistance).

The above-mentioned advantages of the proposed solution are confirmed byexperiment results.

Particularly referring to FIG. 3, a diagram 300 shows a set of workingcharacteristics of the front-rear contact according to an embodiment ofthe present invention (depending on the dopant concentration of thesemiconductor material surrounding the contact trenches across theinsulating layer). In particular, the diagram 300 has a current I[mA] ona left axis of ordinates, a resistance R[kΩ] on a right axis ofordinates and a biasing voltage VM on an axis of abscissas.

For this purpose, two adjacent front-rear contacts are formed in thesame electronic device (both of them connected to its substrate).Biasing voltages V ranging from −5V to 5V are then applied between thetwo front-rear contacts, and the corresponding currents I are measured(with the resistance R that is calculated accordingly).

As can be seen, working characteristics 310 (representing the current)and 320 (representing the resistance) are obtained when the front-rearcontacts are manufactured as described above. The remaining workingcharacteristics 330 (representing the current) and 340 (representing theresistance) are obtained for non-optimized electronic devices withoutthe (more doped) contact region surrounding the contact trenches (i.e.,when the manufacturing process of the electronic device does not providethe implantation processes after the etching of the contact trenches).

As it can be noted, the working characteristic 320 is below the workingcharacteristic 340 (meaning that the resistance R of the front-rearcontact is lower). For example, when the biasing voltage V is equal to2V the resistance R is reduced by about one third (from 15 kΩ to 6 kΩ).

With reference now to FIGS. 4A through 4B, a process is described formanufacturing an electronic device 400 (see FIG. 4B) adapted forgettering of impurities according to a second embodiment of the presentinvention.

Considering in particular FIG. 4A, the same process steps describedabove are repeated until the creation of the contact region 145 (theelements corresponding to the ones of the preceding figures are denotedwith the same references, and their explanation will be omitted for thesake of simplicity). The contact region acts as a gettering zone for anyimpurities of the whole active layer 142.

Moving now to FIG. 4B, one or more insulating trenches 405 are formed asdescribed above (so as to reach the insulating layer 115). Theinsulating trenches 405 are likewise filled with dielectric material,and the whole front surface 150 is covered with a field oxide layer 410suitably planarized (so as to obtain the desired electronic device 400).As can be seen, in this case the field oxide layer 410 covers the wholefront surface 150 (without any contact windows); moreover, no additionalcontact region is formed (from the front surface 150 to the contactregion 145).

The insulating trenches 405 again partition the active layer 142 intomultiple active regions 415, which will be used to integrate the desiredelectronic components (schematically represented in the figure as 420).Moreover, the insulating trench 405 around the contact trenches 120defines an (insulated) gettering region 425, which segregates theimpurities—gettered by the contact region 145 beforehand.

In this way, a significant amount of impurities of the active layer 142is removed from the active regions 415 (intended to house the electroniccomponents 420). This strongly improves the performance of theelectronic components 420, and then of the whole electronic device 400.

With reference now to FIGS. 5A through 5F, a process is described formanufacturing an electronic device 500 (see FIG. 5F) of the selectiveSOI type.

Considering in particular FIG. 5A, the starting material is again an SOIsubstrate 505 (with a semiconductor substrate 510, a semiconductorstarting layer 512, and an insulating layer 115). However, in this casethe insulating layer 515 has a thickness lower than 0.5 μm, andpreferably ranging from 0.2 μm to 0.4 μm (such as 0.3 μm); likewise, thesemiconductor starting layer 512 has a thickness lower than 0.5 μm, andpreferably ranging from 0.1 μm to 0.45 μm (such as 0.3 μm).

Moving now to FIG. 5B, a single contact trench 520 is formed as abovethrough the layers 512, 515 (by means of two substantially anisotropicetching processes—along a vertical direction Y—through a correspondingphotoresist mask 522); the contact trench 520 likewise clears acorresponding front portion of the substrate 510 (defining a bottom wall530 b) and corresponding internal portions of the starting layer 512 andof the insulating layer 515 (defining side walls 530 s). In this case,the contact trench 520 has preferably a square shape, with each sidehigher than 400 μm.

As shown in FIG. 5C, two (or more) dopant implantation processes areagain performed (along directions I titled as above with respect to thevertical direction Y), in order to form heavily doped internal regions540 within the substrate 510 and the starting layer 512 (only shown forthe substrate 510 in the figure). However, in this case the internalregion 540 is of the opposite type of conductivity with respect to thesubstrate 510 and the starting layer 512 (i.e., of the P-type). Forexample, Boron (B) dopant ions are used; preferably, the dopant doseranges from 10¹² ions/cm² to 1016 ions/cm².

The photoresist mask 522 is likewise stripped at the end of theimplantation processes. Referring now to FIG. 5D, a similar epitaxialgrowing process is carried out so as to form an active layer 542 of theN-type again; at the same time, the epitaxial growing process completelyfills the contact trench 520 (without leaving any vacant regions).

During the epitaxial growing process, the dopant ions of the internalregion 540 (shown in the FIG. 5C) diffuse thereby forming an insulatingregion 545 of the P+ type. As can be noted, the insulating region 545encloses the contact trench 520 (across the insulating layer 515) so asto define a PN junction with the substrate 510 and another PN junctionwith the active layer 542.

Moving to FIG. 5E, a field oxide layer 555 is again formed on top of theactive layer 542—except for a portion thereof where a (larger) activearea 557 around the insulating region 545 is desired.

Continuing to FIG. 5F, one or more insulating trenches 558 are formed asdescribed above reaching the insulating layer 515 (so as to obtain thedesired electronic device 500). The insulating trenches 558 againpartition the active layer 542 into multiple active regions 560, whichare fully insulated by the insulating layer 515 and the insulatingtrenches 558. Moreover, the insulating trench 558 shown in thefigure—around the contact trench 520—defines a further active region561; the active region 561 is insulated from the substrate 510 by meansof the PN junctions formed by the insulating region 545 (whenreverse-biased).

The active regions 560 are typically used to integrate high-voltageelectronic components or devices that need fast access time, low leakageand low parasitic capacitance (schematically represented in the figureas 580), so as to benefit from the typical advantages of the SOIstructures. At the same time, the active region 561 is typically used tointegrate low-voltage electronic components or devices that have todissipate heat through the semiconductor substrate (schematicallyrepresented in the figure as 581), which instead would be adverselyaffected by the SOI structure. As a result, it is possible to obtain aselective structure, which is well suited to house both low-voltage andhigh-voltage electronic components.

Naturally, in order to satisfy local and specific requirements, a personskilled in the art may apply to the solution described above manymodifications and alterations. Particularly, although the presentinvention has been described with a certain degree of particularity withreference to preferred embodiments thereof, it should be understood thatvarious omissions, substitutions and changes in the form and details aswell as other embodiments are possible; moreover, it is expresslyintended that specific elements and/or method steps described inconnection with any disclosed embodiment of the invention may beincorporated in any other embodiment as a general matter of designchoice.

For example, similar considerations apply if the device has anequivalent structure (such as with layers having different thickness);moreover, although in the preceding description reference has been madeto a semiconductor substrate and a starting layer of N-type, theconductivity type of these layers may be reversed (i.e., of P-type).

It is emphasized that the described process is not to be interpreted ina limitative manner; particularly, it is possible to use equivalentsteps, to remove some steps being not essential, or to add furtheroptional steps.

Moreover, the starting material may be either a SOI wafer already readyto be processed or a structure formed by conventional manufacturingprocesses.

In any case, the implantation processes after the epitaxial growingprocess are not strictly necessary and they may be omitted in asimplified implementation (even if the performance of the resultingstructure would be reduced).

In any case, different beams of dopant ions can be used during theimplantation processes (even with a different number of them, down to asingle one).

Moreover, nothing prevents using beams, which form a different anglewith the axis of each contact trench (down to zero).

Alternatively, it is also possible to form the contact windows at adifferent angle with respect to the axis of each contact trench;however, nothing prevents having some contact window along the axis of acorresponding contact trench.

It should be noted that although in the preceding description referencehas been made to a specific number of contact trenches (for thefront-rear contact and the gettering region), this is not to be intendedin a limitative manner; however nothing prevents forming a singlecontact trench even in these embodiments of the invention.

Moreover, alternative layouts are feasible (for example, with differentshapes and/or sizes of the contact trenches, or other arrangementsthereof.

Conversely, the use of more contact trenches is contemplated even in theembodiment of the invention relating to the selective SOI structure.

Without departing from the principles of the invention, it is of coursepossible to form more active regions (for the front-rear-contact), moregettering regions and/or more active regions based on the PN-junctionisolation—by means of corresponding insulating trenches.

It should be readily apparent that the proposed structures may be partof the design of integrated circuits. The design may also be created ina programming language; moreover, if the designer does not fabricatechips or masks, the design may be transmitted by physical means toothers. In any case, the resulting integrated circuits may bedistributed by their manufacturer in raw wafer form, as bare dies, or inpackages form. Moreover, the devices may be integrated with othercircuits in the same chip, or they may be mounted in intermediateproducts (such as mother boards). In any case, the integrated circuitsare suitable to be used in complex systems (such as computers).

Having thus described at least one illustrative embodiment of theinvention, various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be within the spirit andscope of the invention. Accordingly, the foregoing description is by wayof example only and is not intended as limiting. The invention islimited only as defined in the following claims and the equivalentsthereto.

1. A method for manufacturing an integrated electronic device, themethod comprising: providing an SOI substrate comprising a semiconductorsubstrate, an insulating layer on the semiconductor substrate, and asemiconductor starting layer on the insulating layer; and epitaxiallygrowing the starting layer to obtain a semiconductor active layer on theinsulating layer for integrating components of the device, forming atleast one contact trench extending from an exposed surface of thestarting layer to the semiconductor substrate before epitaxially growingthe starting layer, wherein each contact trench clears a correspondingportion of the starting layer, of the insulating layer and of thesemiconductor substrate, the epitaxial growing being further applied tothe cleared portions thereby at least partially filling the at least onecontact trench with semiconductor material.
 2. The method according toclaim 1, further comprising: implanting impurities in at least part ofthe cleared portions between the step of forming the at least onecontact trench and the epitaxially growing, the impurities diffusingduring the epitaxial growing to form an interface region enclosing theat least one contact trench.
 3. The method according to claim 2, whereinthe implanting comprises: implanting at least one beam of saidimpurities along a direction forming an angle with an axis of eachcontact trench ranging from 20 to
 450. 4. The method according to claim2, wherein the interface region is a contact region having the same typeof conductivity as and a concentration of impurities higher than thesemiconductor substrate and the active layer, the method furthercomprising the steps of: forming an insulating trench extending from anexposed surface of the active layer to the insulating layer around theat least one contact trench, the insulating trench insulating an activeregion of the active layer from a remaining portion thereof, forming afurther contact region in the active region extending from the exposedsurface of the active layer to the contact region, the further contactregion having the same type of conductivity as and a concentration ofimpurities higher than the active layer, forming an electrical contacton a contact window of an exposed surface of the further contact region,the electrical contact contacting the semiconductor substrate throughthe at least one contact trench, and integrating the components in theremaining portion of the active layer.
 5. The method according to claim4, wherein forming the electrical contact comprises: forming theelectrical contact to have each point of the contact window spaced apartfrom an axis of each contact trench.
 6. The method according to claim 5,wherein the step of forming the electrical contact comprises: formingthe electrical contact to have a line, between each point of the contactwindow and an edge of each contact trench closest to the contact windowat an interface between the insulating layer and the semiconductorsubstrate, forming an angle with the axis of the contact trench higherthan 60°.
 7. The method according to claim 2, wherein the interfaceregion is a contact region having the same type of conductivity as and aconcentration of impurities higher than the semiconductor substrate andthe active layer, the contact region gettering impurities of the activelayer, wherein the method further comprises: forming an insulatingtrench extending from an exposed surface of the active layer to theinsulating layer around the at least one contact trench, the insulatingtrench insulating a gettering region of the active layer segregating thegettered impurities from a remaining portion of the active layer, andintegrating the components in the remaining portion of the active layer.8. The method according to claim 4, wherein the step of forming the atleast one contact trench comprises forming a plurality of contacttrenches.
 9. The method according to claim 8, wherein the step offorming the contact trenches comprises: forming each pair of adjacentcontact trenches spaced apart by a distance ranging from 1 μm to 3 μm,and forming each contact trench with a square transversal section havingeach side thereof ranging from 1.5 μm to 5 μm.
 10. The method accordingto claim 2, wherein the interface region is an insulating region havinga type of the conductivity different than a type of conductivity of thesemiconductor substrate and of the active layer, the method furthercomprising: forming an insulating trench extending from an exposedsurface of the active layer to the insulating layer around the at leastone contact trench, the insulating trench insulating a first activeregion of the active layer from a remaining second region thereof,integrating first components in the first active region, the firstcomponents being insulated from the semiconductor substrate by ajunction formed by the insulating region with the active layer and/orthe semiconductor substrate when reverse-biased, and integrating secondcomponents in the second active region, the second components beinginsulated from the semiconductor substrate by the insulating layer. 11.An integrated electronic device of the SOI type comprising: asemiconductor substrate, an insulating layer on the semiconductorsubstrate, a semiconductor active layer on the insulating layer,components of the device integrated in the active layer, and at leastone contact trench crossing the insulating layer, the at least onecontact trench being at least partially filled with semiconductormaterial.
 12. The device according to claim 11, further comprising: acontact region enclosing the at least one contact trench, the contactregion having the same type of conductivity as and a concentration ofimpurities higher than the semiconductor substrate and the active layer,an insulating trench extending from an exposed surface of the activelayer to the insulating layer around the at least one contact trench,the insulating trench insulating an active region of the active layerfrom a remaining portion thereof, the components being integrated in theremaining portion of the active layer, a further contact region in theactive region extending from the exposed surface of the active layer tothe contact region, the further contact region having the same type ofconductivity as and a concentration of impurities higher than the activelayer, and an electrical contact on a contact window of an exposedsurface of the further contact region, the electrical contact contactingthe semiconductor substrate through the at least one contact trench. 13.The device according to claim 12, wherein each point of the contactwindow is spaced apart from an axis of each contact trench.
 14. Thedevice according to claim 13, wherein a line, between each point of thecontact window and an edge of each contact trench closest to the contactwindow at an interface between the insulating layer and thesemiconductor substrate, forms an angle with the axis of the contacttrench higher than 60°.
 15. The device according to claim 11, furthercomprising: a contact region enclosing the at least one contact trench,the contact region having the same type of conductivity as and aconcentration of impurities higher than the semiconductor substrate andthe active layer, the contact region gettering impurities of the activelayer, an insulating trench extending from an exposed surface of theactive layer to the insulating layer around the at least one contacttrench, wherein the insulating trench insulates a gettering region ofthe active layer segregating the gettered impurities from a remainingportion of the active layer, the components being integrated in theremaining portion of the active layer.
 16. The device according to claim12, wherein the at least one contact trench comprises a plurality ofcontact trenches.
 17. The device according to claim 16, wherein eachpair of adjacent contact trenches is spaced apart by a distance rangingfrom 1 μm to 3 μm, and wherein each contact trench has a squaretransversal section with each side thereof ranging from 1.5 μm to 5 μm.18. The device according to claim 11, further comprising: an insulatingregion enclosing the at least one contact trench, the insulating regionhaving a type of the conductivity different than a type of conductivityof the semiconductor substrate and of the active layer, an insulatingtrench extending from an exposed surface of the active layer to theinsulating layer around the at least one contact trench, the insulatingtrench insulating a first active region of the active layer from aremaining second region thereof, wherein first components are integratedin the first active region, the first components being insulated fromthe semiconductor substrate by a junction formed by the insulatingregion with the active layer and/or the semiconductor substrate whenreverse-biased, and wherein second components are integrated in thesecond active region, the second components being insulated from thesemiconductor substrate by the insulating layer.